How good are you at keeping to a sleep schedule? How important is sleep to you, personally? It might be surprising to know that sleep is far more important for your health than you realise. It’s all down to the circadian rhythms in your body.

Circadian rhythms are involved in many aspects of behaviour and physical health. This includes regulating body temperature, the release of specific hormones, concentration, mood, eating and sleeping. These features are involved in a 24 hour cycle. A disruption in this rhythm has been linked with health problems such as heart disease, obesity, diabetes, some types of cancer, depression and bipolar disorder. 

Night shift workers are at an especially high risk for these issues due to the regular disruption of their circadian rhythm.  This is why working night shift is linked to a shorter life span and an increase in the risk of cardiovascular disease. 

Fun fact: A chronotype is the technical term for a “night owl” or an “early bird”. If you’re more active, and your brain is more awake, during the morning you would fit into the chronotype of early bird like me! 

A team of researchers has recently had a look at whether there is a genetic link between circadian rhythms (rest-activity cycles) and mood disorders such as bipolar disorder. They did this by identifying the sections of the human genome that are linked with circadian cycling. Two sections were identified and it turns out that one of these sections interacts with a gene for bipolar disorder. “Genome-Wide Association Study of Circadian Rhythmicity in 71,500 UK Biobank Participants and Polygenic Association with Mood Instability”

A disruption in the rhythm has been linked with health problems such as heart disease, obesity, diabetes, some types of cancer, depression and bipolar disorder.

However, the team says it found “little evidence of genetic correlation between rest-activity cycles and psychiatric phenotypes… This is surprising given the literature on circadian rhythmicity and mood disorders,” the authors point out.

Instead, the results showed an association between low levels of rest-activity and a higher risk for mood disorders, including mood instability, depression and neuroticism. “Mood instability is a common symptom across several psychiatric disorders and, as such, may be a more useful phenotype than categorical diagnoses for understanding underlying biology,” they point out.  Phenotype = the physical symptoms.

These results will assist further research on the relationships between circadian function and psychiatric disorders. “Circadian rhythm disruption is a core feature of mood disorders and the genetic variants identified in this study may be involved in the pathophysiology of mood disorders …  Several of the genetic variants identified are located within or close to genes which may have a role in the pathophysiology of mood disorders … The possibility of a direct link between genetic loading for circadian disruption and the experience of dysregulated or unstable mood is therefore of considerable interest and merits further investigation.”